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Mozilla is pushing ahead with its efforts to discourage the use of plug-in based content on the Web and gave developers until the end of March to apply for an exemption from the plug-in blocking planned for the Firefox browser.

The company will create a plug-in whitelist, but to get their plug-ins on it developers will need to present a “credible plan” for replacing them with standard Web technologies in the future, Chad Weiner, Mozilla’s director of product management, said Friday in a blog post.

Submissions will be accepted until March 31 and exemptions will be granted for four consecutive Firefox releases. If plug-in authors need additional whitelisting time after those four releases, they will need to reapply and their cases will be re-examined.

Plug-ins act as bridges between the browser and external applications that can render special types of content found on the Web, but which browsers can’t display on their own. The most common plug-ins include those for Flash Player, Java, Adobe Reader and Microsoft Silverlight.

Mozilla revealed its plan to “put users in control of plug-ins” over a year ago, in January 2013, arguing that such programs are a common source of security vulnerabilities, performance issues and browser crashes.

Click-to-play

The company’s solution to the problem is a feature called click-to-play that allows users to manually confirm the execution of plug-ins by clicking on place holders for plug-in based content on Web pages.

Click-to-play has been present in Firefox for some time as an optional, experimental feature in various stages of completion depending on the browser’s version, but Mozilla’s goal is to eventually enforce it by default for all plug-ins, except a few popular ones.

For example, the company said in September that the latest version of Flash Player will be exempted from click-to-play. Mozilla’s reasoning is that Flash content is very common on the Web, and many websites use ‘hidden’ Flash instances that the user does not see and cannot click on. “Making Flash click-to-play would be confusing for most users,” it said.

Baby steps

The new plug-in whitelist announced Friday suggests that Mozilla has decided to take a more gradual approach that will provide developers with more time to migrate away from plug-ins. However, the company’s goal of ridding the Web of plug-in based content remains unchanged.

“We strongly encourage site authors to phase out their use of plugins,” Weiner said. “The power of the Web itself, especially with new technologies like emscripten and asm.js, make plugins much less essential than they once were. Plus, plugins present real costs to Firefox users. Though people may not always realize it, we know plugins are a significant source of poor performance, crashes and security vulnerabilities.”